1. Field of the Invention
The present invention relates to a bearing apparatus, a spindle motor, and a disk drive apparatus.
2. Description of the Related Art
Spindle motors arranged to rotate disks about central axes thereof are typically installed in hard disk apparatuses and optical disk apparatuses. Such spindle motors include a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque centered on the central axis by magnetic flux generated between the stationary and rotating portions, whereby the rotating portion is caused to rotate with respect to the stationary portion.
The stationary and rotating portions of the spindle motor are joined to each other through a bearing apparatus. In recent years, in particular, spindle motors have often been provided with a bearing apparatus in which a lubricating fluid is arranged between the stationary and rotating portions. The structure of a known bearing apparatus using the lubricating fluid is described, for example, in JP-A 2009-136143.
In some bearing apparatuses using the lubricating fluid, a pumping seal including a plurality of grooves is arranged in the vicinity of a surface of the lubricating fluid. Once the spindle motor is started, the pumping seal causes a portion of the lubricating fluid which is near the surface of the lubricating fluid to be drawn inward toward an interior of the bearing apparatus. This contributes to preventing the lubricating fluid from leaking out of the bearing apparatus. JP-A 2009-136143 notes that a pumping seal characterized in having a pumping structure including grooves arranged in a spiral pattern is located between a surface in a rotor component and a surface in a bearing component (see paragraph [0023] and FIG. 1 of JP-A 2009-136143).
In the case of the structure described in JP-A 2009-136143, however, if the area of the pumping seal is increased to increase an effect of the pumping seal, the radial dimension of the bearing apparatus is increased accordingly. Moreover, members which together define the pumping seal are also accordingly increased in radial dimension. This leads to an increase in a loss of torque in the bearing apparatus.